Divider blocks are used to distribute a fluid at high pressure and low volume. Divider blocks are described, for example, in U.S. patent application Ser. No. 10/816,212, filed Apr. 1, 2004, which is hereby incorporated by reference. Because the amount of fluid that a divider block dispenses during each cycle can be calculated from the piston size and stroke, the amount of fluid dispensed by a divider block in a period of time can be determined using a cycle indicator that counts the number of cycles the divider valve completes within the time period. U.S. Pat. No. 5,835,372, issued Nov. 10, 1998, describes a device for indicating cycles of divider blocks and is hereby incorporated by reference. Such cycle indicators typically have a piston follower that extends into a cylinder of the divider block through a seal and is pushed against the piston by a spring in the indicator. As the piston moves back and forth, the piston follower moves a magnet that activates a reed switch or a Hall effect sensor to indicate a cycle of the divider block.
There are several disadvantages of prior art cycle indicators. One disadvantage is that over time, fluid tends to leak past the seal through which the piston follower extends. In a typical arrangement the piston follower extends through an O-ring seal and moves relative to it as the piston follower reciprocates. After prolonged use, fluid starts to leak past the O-ring seal. Even though only a small amount of fluid may leak past the seal continued leakage can eventually cause damage to the compressor. For example, a Number 18 divider block that dispenses 30-weight oil at room temperature dispenses about six drops of oil or about 0.018 of a cubic inch for each stroke of the piston. Continued leakage could result in the loss of as much as 50 percent or more of the piston's oil output.
Another disadvantage of prior art devices is the piston follower reduces the total volume in the cylinder so the dispensing valve dispenses less fluid from the cylinder. This decreased volume of fluid dispensed can mean insufficient lubrication for the lubricated device.
Another disadvantaged of most prior art cycle indicators is that they only indicate that a cycle has occurred, but not how far the piston has moved. It is important for the operator to be able determine movement of the piston because such movement indicates whether or not the correct quantity of oil is moved out of the piston cylinder bore. For example, a short piston cycle indicates that not enough oil is being supplied to the lubricated point, which may cause premature wear or failure of the component.
Some attempts have been made to overcome the above-described problems. One such attempt includes a cycle indicator that utilizes a snap-action design with colored tape that disappears to indicate a cycle. In use, as the cylinder piston approaches the end of the cylinder a magnet causes an indicator to snap into place. Such cycle indicators are completely sealed in that the cycle indicator housing is sealed to the divider block and the fluid is allowed to bypass the piston follower, thus, eliminating fluid leakage. However, such a design does not work for all types of divider blocks and has been subject to failures in use. This design indicates only that a cycle has occurred, and does not provide an indication of actual piston stroke.
Another prior art uses balls in a transparent housing surrounding the piston follower. A magnet causes the balls to track the movement of an internal magnet. The balls, however, tend to get stuck in their races.
Industry still has a need for a reliable cycle indicator that can provide information about actual piston travel.